1. Field of the Invention
This invention relates to an apparatus and method for effectively measuring and monitoring the filming level on a photoreceptor.
2. Description of the Related Art
Sensors have been used for many purposes in electrostatographic printing machines. For example, U.S. Pat. No. 5,574,527 describes a method and apparatus for sensing multiple process parameters with a single sensor in a printing machine. It is described that the sensor can be used to sense the photoreceptor belt seam to insure that the latent image is not formed on the photoreceptor belt seam, to sense the toner density to control the toner dispenser, to sense the photoreceptor charging, developer bias, image exposure and image processing systems, to sense the presence of copysheets in a paper transport, and to sense the type of copysheet. The sensor is described to be uniquely located in the printing machine in order to function as described. Sensing of photoreceptor filming with the sensor is not described.
Most typically, infrared densitometers such as extended toner area coverage sensors are used in association with developing stations to monitor the toner density on the photoreceptor in order to control the amount of toner dispensed.
U.S. Pat. No. 5,903,797 describes a method and apparatus for monitoring cleaning performance to predict printing machine cleaner life. The method and apparatus employ a sensor and artificial stress conditions to determine the cleaner brush life. In the method, a comparative analysis is done between the data from the monitoring of a normal cleaning residual toner particle mass and the data from the artificial stress conditions cleaning residual toner particle mass to predict brush cleaner life reliably. The monitoring is conducted in a non-printing area of the photoreceptor. It is described that degradation in the ability of the cleaning brush to remove toner particles from the photoreceptor becomes detectable under the artificial stress conditions. Monitoring of filming on the entire photoreceptor surface under normal printing conditions is not described.